4. House-keeping genes and luxury genes House-keeping genes: Expressed in all cell types, essential for all cels Luxury genes: Tissue-specific genes, expressed in special cells Sequential expression of various genes in early Drosophila embryo4. House-keeping genes and luxury genes House-keeping genes: Expressed in all cell types, essential for all cells Luxury genes: Tissue-specific genes, expressed in special cells Sequential expression of various genes in early Drosophila embryo